> Sometimes mistakes happen(a faulty system, a design bug or straight out human error and people who are trying to take advantage of those), most of the time these are correctable.
These errors are correctable if the counter-parties trust each other, or at least have a relationship that they don't want to undermine by being petty.
Immutable blockchain systems are valuable in part because they allow entities to transact with each other even if they don't trust each other at all, don't know each other at all, or are even antagonistic with each other. Yes, if something goes wrong, a transaction won't be reversed, but without the blockchain these potentially antagonistic entities wouldn't have the capacity to do business with each other in the first place.
Blockchains allow these entities capture the value of transacting with each other—value that wouldn't otherwise be realized—at the expense of irreversibility.
You can potentially imagine that if antagonistic entities tried to do business in a more malleable environment, a request to reverse an error by one entity might not be honored by the other entity, or one entity might maliciously attempt to reverse a transaction that was not performed in error, but was simply disadvantageous in hindsight.
The possibility that a transaction may need to be reversed—or that a reversal request may need to be litigated—increases transaction costs, especially when counter parties are antagonistic. The certainty of irreversibility creates a context by which certain entities are willing to do business with each other, when they might not otherwise do business at all.